The invention relates to an electric field sensor called and E-field sensor. E-fields sensors are devices shown by Cehelnik, Zank et. al, and Beatty as being capable of detecting electric fields fluctuations. These may occur from source fields caused by body stepping motion, the charging of bodies from the triboelectric effect, and changes in the background fields. Cehelnik taught about the usefulness of using the AC field of the background signals to detect a proximate body. Cehelnik has also shown the usefulness in using the correlation between the DC field and AC field signatures when a grounded body approaches an E-field sensor with a charged item in hand. Now herein this application, Cehelnik describes and claims usefulness of a sensor having extreme DC E-field sensitivity. The new sensor unexpected exhibits high DC swing voltages with a single stage amplifier and it AC coupled output exhibits the effect of drastically reducing the AC background signal due to a proximate ungrounded body. Thus the sensor provides a new correlated response between the DC E-field input and the AC output of the sensor. Sensing methods using this correlation are claimed, as well as apparatus using the new sensor design.
The correlation effect is seen for transient responses. Transient responses can be caused by the approach of a body proximate to the sensor or occur when a body or background field changes its charge with respect to time. The sensor also allows detection of static or quasistatic effects due to a body approaching the sensor and remaining stationary proximate it. These effects are also observed when the sensor is located behind materials, allowing the sensor to have a see-thru ability.
The need exist to have even more simple e-field amplifiers circuitry to facilitate miniaturization. Further reduction in complexity will facilitate the use of semiconductor deposition processes, perhaps even those used on flat screen TV and video screens. Microsensor arrays will become available by using integrated circuit manufacturing processes.
The resulting sensor arrays then will find further uses when embedded within object. Even humans bodies may have embedded sensors such as in the brain or other tissues. These embedded sensors will detect local changes in electric fields due to a variety of mechanisms such a nerve responses or electric response, thus allowing for high resolution E-field imaging.
Further simplified and more sensitive sensors will find usefulness in the systems as described by the author's previous applications, such as in human machine interfaces, imaging, and security systems.
APPROACH
The invention achieves extreme E-field sensitivity to changing electric. This is found due to the high input impedance of a JFET type junction used in operational amplifiers and some discrete components. For example the TL082 has an input impedance of order 1012 Ohms, and even other exist with higher input impedance. The trouble is these amplifiers require some flow of current from their inputs to bias the amplifiers properly or they will saturate or in other words have a large DC offset. An E-field sensor picks up an E-field with an electrode attached to the input of the amplifier. To date sensor amplifier designs use a shunt resistor to allow for DC bias of the operational amplifiers.
Zank et. al. shows the importance in increasing the impedance of the shunt resistor. Cehelnik shows the usefulness of the filtering effect of the resistor and shunt capacitances.
Herein it we show the elimination of the bias resistor results in some unexpected and useful results of high DC sensitivity. Even further advantages are obtained when there is electrical coupling between the opamp E-field input and the voltage supply rail of the amplifier.
KEY FEATURES OF INVENTION
A key capability of the invention is have extremely high input impedance of the amplifier by allowing the DC signal output of the amplifier to have a bias even toward saturation, say the negative voltage rail of the TL082. This amplifier in this mode is partial turned on and amplifies small AC signals that ride on the bias, but is not operational in the usual sense. It therefore also draws very little power when in this state. This operation mode is in contrast to conventional operation.
Another key feature of the invention is the amplifier has electrical coupling between the E-field input to the amplifier and a voltage rail.
The said coupling causes the amplifier to turn on with the approach of a body or changes in the E-field, because during the event the coupling causes the amplifier to turn on.
Yet another key feature of the invention is there are two outputs, a DC coupled output of the amplifier, and another that is AC coupled. Each of these output are coupled to optional filter for shaping of the responses.
Another feature sensor input is an antenna coupled through an impedances network to the positive input in a buffer amplifier. In particular a series capacitor is used, that reduces the capacitance of the antenna, prevents DC burnout of the amplifier, and forms a high pass filter between the antenna and the internal input impedance of the amplifier. It is conceivable that other coupling networks will also find usefulness by others in the art and are also covered in this invention.
However, FIG. 1 shows that there is a pickup electrode that couples the E-field signal through an impedance to the negative voltage supply. The coupling is shown to be through the air and the stray impedances of the wiring circuit.